Introduction

Plastics are labeled by six common recycling codes because there are six different molecules in common use. We call them all "plastic", but they have different properties based on their molecular structure. This activity focuses on the property of density, as a way to separate out a mixed collection of the six common kinds of plastics.

Activity

Check your tray. It should contain a cup with 6 different plastic pellets, a test tube labeled "Alcohol", a test tube labeled "Water", a stirring rod, and a plastic pipette. Put a check mark in the Box 1 when you have identified them all.

Describe the pellets. Each plastic pellet has a different shape and/or color to distinguish it from the others, . In Box 2, describe the six pellets.

Density Test I. Some of the pellets are more dense than water. Drop the pellets into the water test tube and see which sink. In Box 3, identify the pellets that sank, and in Box 4, identify the pellets that sank, using the descriptions you made in Box 2.

Density Test II. Some of the pellets are less dense than alcohol. Use the pipette to add alcohol to the water a little at a time, swirling the test tube to mix. The pellets will begin to float when then density of the liquid matches the density of the pellet. In Box 5, list the pellets in the order that they rose to the surface, using the descriptions you made in Box 2.

Analysis

Write up a procedure that would effectively separate all six of the plastic pellets. Explain what you would look for in the liquids you would use. You may like to use the following format to get started: